External monitor not working in clamshell mode after resolution change

ViktorTomka wrote:

The docking station is very professional and compatible with Mac.

I would not describe a "universal docking station" that works with USB-A hosts and that relies on DisplayLink or other workarounds as "very professional."

That's a low-end dock – even lower-end than plain USB-C docks that offer a single video port, but which always drive that port off first-class, hardware-accelerated, DisplayPort Alt Mode output.

My laptop is a MacBookAir M4 2025.

You didn't say whether it is a 13" or 15" model, but both have the same external display support.

MacBook Air (13-inch, M4, 2025) - Tech Specs – Apple Support

MacBook Air (15-inch, M4, 2025) - Tech Specs – Apple Support

"Simultaneously supports full native resolution on the built-in display at 1 billion colors and up to two external displays with up to 6K resolution at 60Hz

Thunderbolt 4 digital video output

Support for native DisplayPort 1.4 output over USB-C"

Your MacBook Air has the ability to drive two monitors with 4K @ 60 Hz resolution (like your 32" Samsung Smart Monitor M7) using first-class hardware-accelerated video output. There is no need to use DisplayLink – or other similar workarounds – and incur the associated disadvantages unless you are trying to drive more monitors than your Mac's hardware is designed to support.

You might want to try plugging that 32" Samsung Smart Monitor M7 directly into your Mac, using a high-quality USB-C to USB-C cable that is as short as possible, and whose description says that it is rated to carry 4K video.

ViktorTomka wrote:

Hi, thank you very much for the information. I contacted i-tec. Yes, DisplayLink needs to be installed, and I have also updated it. I'm just surprised that it worked fine for a year and then suddenly stopped working. My laptop is an M4 2025 15". Can you recommend a docking station?

If it was working, and is not working now, there are a few possibilities:

• One is that there was an update to macOS that broke the DisplayLink drivers. My understanding is that when this happens, it is up to the third-party vendor (or their "arms supplier", in this case, Synaptics) to fix it.
• Another might be that some macOS preference files that keep track of display configuration got corrupted. If this is the issue, it might be possible to fix the issue by manually deleting those files and restarting the Mac, to get it to generate new ones.
• A third might be that you changed which port on the dock you used to connect the monitor, and it matters.

As for a replacement docking station, it depends on your needs.

Plain USB-C docks that have a single HDMI port, drive it off DisplayPort Alt Mode output, and support 4K @ 60 Hz are inexpensive, generic, and a dime a dozen. Any of these which have their own power supply and all of the other ports that you need (e.g., USB ports, memory card slots, Ethernet ports) are likely to be OK. I would suggest that, in addition to checking the 4K @ 60 Hz specification, you also check how much power a dock can provide to your MacBook using USB-C Power Delivery. If you can find out which versions of HDMI these types of docks support, my suggestion would be to choose a dock that supports HDMI v2.0 (like your Samsung monitor does) over a dock that just supports the older HDMI v1.4.

Thunderbolt docks and hubs can handle higher data rates. This makes them more expensive, but Is also why the Mac is willing to drive one 5K @ 60 Hz monitor or two 4K @ 60 Hz monitors off a single Thunderbolt hub or dock. If you are in the market for a Thunderbolt hub or dock (and I'm not saying that you need one), I'd suggest looking at the offerings on the Other World Computing, SonnetTech, and CalDigit Web sites. While I have not used their Thunderbolt products, all three vendors have provided Thunderbolt products to Mac users for many years.

I would suggest getting a USB-C to HDMI cable or adapter and connect the display directly into the MacBook Air.

This will help determine if the hub may be an issue.

Check the Samsung display for the resolutions that it supports. Some displays can handle pretty much any resolution you throw at them but others will only accept a certain set of display values.

BTW, what model (year) and processor is the MacBook Air?

ViktorTomka wrote:

Dear Apple Support,

Note that this is not Apple Support. There are some people here who help out with display issues – but the people you are talking to are other Apple users,, like yourself.

For reference, here is the hardware I am using:

Docking station:

https://www.alza.cz/i-tec-usb-3-0-usb-c-thunderbolt-dual-display-docking-station-pd-100w-d7935289.htm

I can't run the URL successfully through Google Translate – the translated page chokes at the "Verify that you are human" step.

Running text through piecemeal, I get

"i-tec USB 3.0/USB-C/Thunderbolt Dual Display Docking Station, PD 100W"

"Docking station - USB-C laptop power connector (USB 3.2 Gen 2 (3.1)), fast Power Delivery 100 W, input ports 2× USB–C 3.2 Gen 2, 2× HDMI 2.0, 2× DisplayPort 1.2, 3.5mm audio Jack, multiple monitor support, LED indication, on/off switch and monitor mount, fast charging and Power Delivery 3.0, material plastic, dimensions 2.7 × 8.8 cm (W×H), weight 330 g"

"Universal docking station i-tec USB-C Dual Display for up to two monitors

Universal docking station i-tec USB-C Dual Display. Its key advantage is the ability to output up to 2 video outputs from one USB-C connector. All you need is for your laptop/tablet/phone to have a free Thunderbolt 3 or USB-C port that can transmit a video signal. The package also includes an adapter for connecting to older USB-A ports."

That adapter "for connecting to older USB-A ports is a huge potential red flag. USB-A was never designed to carry video, so any time you see a hub or dock that supports video output when connected to a USB-A host port, that is an indication that the device relies on a second-class workaround at least part of the time. Such workarounds only work when you have a special driver installed on the computer; if you do not have that driver, or if there has been a change in the OS that breaks the driver, you get no video output.

This dock has four places to plug in monitors (two DisplayPorts, two HDMI ports). Macs will only support hooking up one monitor to a plain USB-C dock, or two to a Thunderbolt one. (The rules might one day be different if both the Mac and the dock support Thunderbolt 5, but I'm pretty sure we're not talking about that here!)

I'm not sure that this is a Thunderbolt device. Vendors often use phrases like "Thunderbolt compatible" or "works with Thunderbolt" in describing plain USB-C devices, because Thunderbolt 3 – 5 ports generally also support the USB and DisplayPort Alt Mode protocols that low-end docks/nubs and many video adapters use.

On the iTec site, I found several docks under the "2 monitors" / "supports USB 3.0" category. This looks like it may be the same as the one to which you linked.

I-tec – -tec USB-A / USB-C / Thunderbolt Dual Display Docking Station Gen2 + Power Delivery 100W

Looking at the English-language data sheet for this device, I am even more convinced that it is not a Thunderbolt device, and that it uses either

• A second-class workaround (that requires a special driver), or
• DisplayPort MST (which the Mac doesn't support), or
• Both

to drive some of its video outputs.

When I look at the Quick Start guide, it refers to installing DisplayLink Manager (which would only make sense at all if this dock uses the DisplayLink workaround at least part of the time).

Monitor:

https://www.alza.cz/32-samsung-smart-monitor-m7-cerna-d7056366.htm

That appears to be a 32" Samsung Smart Monitor M7 with a resolution of 3840x160 pixels, and a refresh rate of 60 Hz. It would appear to be the same as

Samsung – 32" Smart Monitor M7 (M70D) 4K UHD with Streaming TV, Speakers and USB-C

According to the Samsung site, the monitor has one USB-C input and two HDMI v2.0 inputs. Modern Macs do not like to see display transmission errors, and may cut signal when they see any. So, if you connect a monitor using a cable that is of marginal quality or that is too long, that can cause the signal to drop out.

However, my inclination would be to think that the problem has something to do with that i-tec dock.

If the monitor doesn’t fit well (like wrong resolution, fuzzy text, flickering, not waking properly, or the HDMI connection acting up), it can definitely cause constant frustration. Before buying a new one, though, here are a few things you could try first:

Check your adapter/hub — sometimes the issue isn’t the monitor but the HDMI adapter or hub. If it’s older or cheap, it might not support your Mac’s resolution or refresh rate properly.

Adjust display settings — go to System Settings > Displays, click your external monitor, and try “Optimize for external display” or manually pick a different resolution/refresh rate.

Close lid properly — make sure your MacBook’s lid is fully closed and it’s plugged into power, otherwise clamshell mode can act flaky.

Wake trick — sometimes, plugging in the keyboard or moving the mouse wakes it better than using the power key.

Try a different cable — especially if you’re using HDMI, cheap cables can cause weird signal drops.